Organic compounds which are grafted with fluorinated olefins and contain groups which are adsorbed on metal surfaces are excellent additives to lubricants for reducing wear and/or friction between moving parts.
Lubricants of various sorts are widely used in systems containing moving parts which rub against one another, and are primarily used to reduce wear between the parts and/or reduce friction between the parts, usually both. Secondarily they may perform other functions, such as protecting metal parts from corrosion. While a xe2x80x9cbasexe2x80x9d material is usually used for the majority of a lubricant composition, various additives are usually also used in the composition, such as additives to reduce wear, reduce friction, prolong the life of the lubricant, make the lubricant useful over a wider temperature range, and for many other purposes. Therefore, improved (in price and/or lubricant properties) additives are constantly being sought.
The use of various fluorinated organic compounds in lubricant systems is known in the art, see for instance U.S. Pat. Nos. 2,433,844, 5,391,814 and Japanese Patent 2,604,186. However, many of these compounds have the disadvantage of being pure compounds (or defined mixtures thereof) which are expensive to synthesize, and therefore expensive to use. It would be preferable to use compounds which are relatively simple and therefore cheap to make, and to use these in relatively small quantities in lubricant systems, to keep cost down.
U.S. Pat. No. 2,562,547 describes the grafting of a variety of organic compounds with certain fluoroolefins such as tetrafluoroethylene (TFE), and uses for the various fluorinated products. The use of certain of these types of compounds as unexpectedly superior lubricant additives is not described.
U.S. Pat. No 5,032,306 describes the use of hydrocarbons grafted with perfluoroolefins as lubricants in certain refrigeration systems. No mention is made of grafting compounds which contain functional groups.
This invention concerns a composition comprising:
(a) a major portion of a lubricant base; and
(b) a minor portion of a first lubricant additive which is an organic compound which is grafted with one or more fluorinated olefins and which, when combined with a lubricant base, forms a lubricant;
and provided that:
said additive contains at least 5 percent by weight of fluorine; and
said organic compound contains at least one functional group which can be adsorbed on a metal surface and wherein said functional group is selected from the group consisting of carboxylic esters, carboxylic acids, carboxylic amides, imides, amines, phosphoric acid derivatives, phosphonic acid derivatives, dithiophosphate esters, ethers, hydroxyls, carbonates, thio derivatives thereof, and heterocyclic groups.
The invention also concerns an apparatus, comprising:
(a) a first part which is metal;
(b) a second part which is in apparent contact with said first metal part, and said first part and second part move with respect to one another; and
(c) a lubricant which comprises:
(i) a major portion of a lubricant base; and
(ii) a minor portion of a first lubricant additive which is an organic compound which is grafted with one or more fluorinated olefins and which, when combined with a lubricant base, forms a lubricant;
and provided that:
said additive contains at least 5 percent by weight of fluorine; and
said organic compound contains at least one functional group which can be adsorbed on a metal surface and wherein said functional group is selected from the group consisting of carboxylic esters, carboxylic acids, carboxylic amides, imides, amines, phosphoric acid derivatives, phosphonic acid derivatives, dithiophosphate esters, ethers, hydroxyls, carbonates, thio derivatives thereof, and heterocyclic groups.
Herein certain terms are used, some of them relating to lubricants. Lubricant technology is well known in general, see for instance E. R. Booser, Ed., CRC Handbook of Lubrication, Vol. II, CRC Press, Inc., Boca Raton, Fla., U.S.A., (1983), p. 229-315; D. Klamann in B. Elvers, et al., Ed., Ullmann""s Encyclopedia of Industrial Chemistry, Vol. A15, VCH Verlagsgesellschaft mbH, Weinheim, Germany (1990), p. 424-511; R. M. Mortimer, et al., Ed., Chemistry and Technology of Lubricants, VCH Publishers, New York, 1992; all of which are hereby included by reference. Herein the following terms are defined as:
A lubricant base is a material that is the majority of the component of the lubricant system, and which reduces friction and/or wear between the moving components being lubricated, and may also have other useful functions. Useful lubricant bases include petroleum derived (sometimes also called mineral) lubricants, synthetic hydrocarbons, polyether oils, carboxylic esters, phosphoric acid esters, silicone containing oils, and halogenated hydrocarbons and halocarbons. Petroleum derived and synthetic hydrocarbon lubricant bases are preferred and petroleum derived lubricant bases are especially preferred.
A lubricant additive is a chemical which improves the wear-reducing ability or decreases the friction of a lubricant base when a state of hydrodynamic lubrication cannot be maintained. Common lubricants provide for a liquid film between parts moving with respect to one another. This is called hydrodynamic lubrication. As long as a full hydrodynamic liquid film is maintained between the parts, wear will be minimized and friction will be determined entirely by the properties of the fluid film. Hydrodynamic lubrication is often difficult to achieve and maintain in practice. Many lubricants, such as mineral oils, found to be highly effective under hydrodynamic lubricating conditions exhibit seriously degraded performance when conditions depart therefrom. It is for this reason that lubricant additives are necessary. Addition of lubricant additives to lubricant bases results in lubricant compositions which exhibit excellent lubricating performance over a wide range conditions in use. The present invention is directed to a particular class of compositions, hereinbelow described, which have surprisingly been found to be highly effective as lubricant additives.
By an organic compound is meant a compound which contains at least one hydrogen atom bound directly to a carbon atom.
By a functional group is meant any group or moiety containing an element other than carbon, hydrogen and fluorine. These are sometimes called xe2x80x9cpolar head groupsxe2x80x9d. See for instance J. A. Crawford, et al., in R. M. Mortimer, et al., Ed., Chemistry and Technology of Lubricants, VCH Publishers, New York, 1992, p. 165, and A. J. Groszek, Interdisciplinary Approach to Lubricant Technology, NASA SP-318 1973, p. 477-525, both of which are hereby included by reference.
By adsorbed on the metal surface is meant that the functional group concerned (and hence the compound which contains that functional group) is attracted to a metal surface with energies in excess of ordinary Van der Waals forces, as exhibited by hydrocarbons such as n-alkanes. The molecule which contains the functional group is often a so-called amphiphile, which has the functional group, and another part of the molecule is compatible with the lubricant base being used. The use of these amphiphiles as lubricant additives and associated topics are also discussed in M. Salmeron, Chemtech, September 1998, p. 17; H. A. Spikes, Langmuir, vol. 12, p. 4567 (1996); M. K. Chaudry, Current Opinion Colloid Interfacial Sci., vol. 2, p. 65 (1997), all of which are hereby included by reference. This adsorption may be measured by adsorbing the compound containing the functional group on the metal surface from a solution in n-alkane, as described in A. J. Groszek, Interdisciplinary Approach to Lubricant Technology, NASA SP-318 1973, p. 477-525. Such forces can include covalent or coordinative bonding, electrostatic or coulombic interactions, and hydrogen bonding. This metal surface herein includes not only the metals themselves, but any other layer normally present on the surface of a particular metal, such as an oxidation layer. For example, aluminum typically has a layer of aluminum oxide (which may be partially hydrated) on its surface.
By a fluorinated olefin is meant any olefin containing at least one fluorine atom. Such an olefin may contain one or more ether groups, and includes vinyl ethers.
By grafting herein is meant that one or more molecules of the fluorinated olefin is covalently bonded to the organic compound by a free radical, anionic or other process, and preferably a free radical process.
By xe2x80x9capparent contactxe2x80x9d is meant that the surfaces appear to contact each other, but may in fact be separated slightly, as by a film of lubricant or an adsorbed film of additive.
The organic compound which is suitable for use as a lubricant additive according to the present invention has at least one functional group which can xe2x80x9cpreferentiallyxe2x80x9d adsorb onto a metal surface, preferably a metal which is actually being used in an apparatus being lubricated. Useful functional groups include carboxylic esters, carboxylic acids, carboxylate salts, carboxylic amide, imide, amine, phosphoric or phosphonic acid derivatives such as esters, dithiophosphate ester, ether, hydroxyl, carbonate, hetereocyclic groups (such as N, S and/or O compounds), sulfonic acids that their salts, and analogous sulfur compounds such as thioamides and thioesters. Such functional groups are known in the art, see for instance R. M. Mortier, et al., Chemistry and Technology of Lubricants, VCH Publishers, New York, 1992, p. 165; and A. J. Groszek, Interdisciplinary Approach to Lubricant Technology, NASA SP-318 1973, p. 477-525, which are hereby included by reference. Preferred functional groups are carboxylic ester, carboxylic acid, hydroxyl, and carboxylic amide, and carboxylic ester, and carboxylic acid are more preferred, and carboxylic ester, is especially preferred. There may be more than one functional group in the organic compound and if more than one, they may be the same or different. Dicarboxylic esters are also especially preferred.
In one preferred form the organic compound (before grafting) has a boiling point at atmospheric pressure of greater than about 150xc2x0 C., more preferably greater than about 200xc2x0 C., and especially preferably greater than 250xc2x0 C. In another preferred form the additive (organic compound after grafting) has a boiling point at atmospheric pressure of greater than about 150xc2x0 C., more preferably greater than about 200xc2x0 C., and especially preferably greater than 250xc2x0 C. In another preferred form the organic compound has a molecular weight of about 100 to about 3,000, more preferably about 250 to 1,500. Grafted polymers, especially those of lower molecular weight, may also be used.
Any fluorinated olefin that may be free radically grafted onto the chosen organic compound may be used. Such fluorinated olefins are known in the art, see for instance U.S. Pat. Nos. 2,562,547 and 5,032,306 both of which are hereby included by reference. The grafting may also be initiated by thermally, photochemically and by irradiation, see B. Ameduri, et al., in Topics in Current Chemistry, Vol. 192. Organofluorine Chemistry, Fluorinated Alkenes and Reactive Intermediates, Springer-Verlag, Berlin, 1997, p. 165-233, which is hereby included by reference. In one preferred form the fluorinated olefin is perfluorinated. In another preferred form it has the formula R1R2Cxe2x95x90CR3R4 wherein R1 is chlorine, fluorine or hydrogen, R2 and R4 are each independently fluorine or hydrogen, R3 is fluorine, hydrogen, alkyl or fluorinated alkyl, provided that at least one of R1, R2 and R4 are fluorine or R3 is fluorinated alkyl. It is more preferred that R1, R2 and R3 are fluorine, and R4 is fluorine or perfluoro-n-alkyl containing 1 to 10 carbon atoms. In another preferred form, the fluorinated olefin has the formula F2Cxe2x95x90CFOR5 wherein R5 is fluorinated alkyl, more preferably perfluoro-n-alkyl containing 1 to 4 carbon atoms. Useful fluorinated olefins include vinyl fluoride, vinylidene fluoride, trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene (HFP), 3,3,4,4,5,5,6,6,6-nonofluoro-1-hexene (PFBE), perfluoro(methyl vinyl ether) (PMVE), perfluoro(n-propyl vinyl ether) (PPVE), 3,3,3-trifluoropropene,1,1,3,3,3-pentafluoropropene, and 1,2,3,3,3-pentafluoropropene. Preferred fluorinated olefins are TFE, chlorotrifluoroethylene, HFP, PFBE, PMVE, vinylidene fluoride, trifluoroethylene, and PPVE, and more preferred fluorinated olefins are TFE, HFP and PMVE, and TFE is especially preferred.
The grafting reaction is initiated by typical free radical generators such as organic peroxides. Such processes are known in the art, see for instance U.S. Pat. Nos. 2,562,547 and 5,032,306. The procedures described in these references and in the appropriate examples herein illustrate how to carry out these grafting reactions. These grafting reactions usually graft the fluorinated olefin in a random manner, although some positions in the organic compound being grafted may be more favored than others. Some of the organic molecules may be ungrafted, especially if no separation is done on the crude mixture obtained after grafting. Such a separation may be difficult and expensive due to the high boiling point of many of the useful organic compounds. The total amount of fluorine in the grafted compound is based on the weight of the total grafted compound including ungrafted organic molecules when they are present. The fluorinated groups grafted onto the organic compound may contain one or more molecules of fluorinated olefin, depending on the fluorinated olefin used, the organic compound used, the free radical source used, and the grafting conditions. The total amount of fluorine in the grafted organic compound will also be affected by these variables. The grafted organic compound suitable for use as a lubricant additive according to the present invention should contain at least about 5 weight percent fluorine, preferably at least about 8 weight percent fluorine, and more preferably at least about 15 weight percent fluorine (elemental analysis). Preferably the grafted organic compound should be a liquid.
The grafted olefin compound suitable for use as a lubricant additive according to the present invention is combined with a lubricant base to form a lubricant. The major portion of this composition by weight, based on the total amount of lubricant base and grafted olefin compound present, is the lubricant base, and the minor portion is the grafted olefin compound. Preferably the amount of grafted olefin compound is such that the amount of fluorine in the lubricant (base lubricant plus grafted olefin compound) from the grafted olefin compound is about 200 ppm to about 10 percent by weight, more preferably about 500 ppm to about 3 percent by weight, and especially preferably about 0.10 to about 1.0 percent by weight. Preferably also the base lubricant and grafted olefin polymer form a single liquid phase at the lubricant use temperature, and/or the entire lubricant composition forms a single liquid phase at the lubricant use temperature.
Preferably the grafted olefin compound and base lubricant should not react with one another to form deleterious products (of course at high operating temperatures lubricants may degrade but this is not included in this statement). A particular functional group may react with a particular lubricant base, but usually a suitable combination of either a particular grafted organic compound or particular lubricant base with a counterpart can be found with minimal experimentation. Such a reaction at times may be benign or even beneficial.
The lubricant composition of the invention, comprising a lubricant base and a lubricant additive may include other additives that are conventionally added to lubricants for various purposes. These include oxidation inhibitors (including antioxidants and metal oxidation inhibitors), viscosity index improvers, pour point depressants, detergents and dispersants, extreme pressure additives, demulsifiers, corrosion inhibitors, emulsifiers and emulsifying aids, dyes and deblooming agents, fluorescent additives, antifoam agents, and (other) antiwear and friction modifiers. The entire lubricant may be a solid, semisolid (grease) or liquid at room temperature, but is preferably a liquid at the operating temperature of the thing being lubricated.
Lubricants are generally employed where two parts are in contact and move with respect to one another. For the lubricants containing the grafted organic compound it is preferred that at least one of the parts, and preferably both of the these parts are metallic. It is also preferred that for the particular metal present the functional group of the additive adsorbs to that metal. The choice of (a) functional group(s) is often not critical in this respect, although a particular functional group may be better with some metals than others.
If a nonmetallic part is part of this apparatus, it may be a ceramic, a thermoplastic, or a thermoset. Any combination (xe2x80x9ccompositexe2x80x9d) of metals and any of the nonmetallic materials may also be used. If nonmetals are used, they may bear functional groups which can interact with the functional group of the additive. Metals useful for the moving part(s) include ferrous metals such as steel, stainless steel and cast iron, aluminum, and zinc and zinc alloys such as die cast metals, titanium, vanadium, chromium, molybdenum, nickel, lead, tin, copper, and their alloys, such as bronze and brass. Preferred metals are ferrous metals. The metal of the two parts may be the same or different. Of course more than two moving parts may be present in such an apparatus.
The lubricant may be distributed to the places where it is needed by conventional means, such as a lubricant (oil) pump, or just be present where needed.
In the Examples, the following abbreviations are used:
HFPxe2x80x94hexafluoropropylene
PFBExe2x80x943,3,4,4,5,5,6,6,6-nonafluoro-1-hexene
PMVExe2x80x94perfluoro(methyl vinyl ether)
TFExe2x80x94tetrafluoroethylene
VF2xe2x80x94vinylidene fluoride
Samples were tested using the ball-on-cylinder (BOCLE) test, described in ASTM D5001, as modified. Several modifications were made to the test, as summarized in Table 1. These changes are expected to make the test a more severe test of anti-wear and friction modifying properties, as described below.
The relative performance of the materials of the present invention as additives in a mineral oil base fluid was evaluated. A commonly available high-quality solvent-refined 150 neutral oil (150N), about ISO 32 viscosity grade, was used. A grade of oil such as 150N might be used as one component for blending of an oil for use in an internal combustion engine. The 150 N contains no additives. This 150N oil was tested according to the modified BOCLE method numerous times, and the average of these results is summarized in Table 2.
For comparative purposes, the friction and wear performance of several fully formulated (ILSAC GF-1), commercially available passenger car motor oils were measured. The oils tested included two leading full synthetics (MOBIL(copyright) 15W30, Castrol(copyright) SYNTEC(copyright) 5W50) and one conventional non-synthetic oil (MOTORCRAFT(copyright) 5W30). Performance of all three oils was very similar, as summarized in Table 3. This may be because all three contain similar amounts of zinc dialkyldithiophosphate (ZDDP), an extremely effective anti-wear agent.